It has long been customary practice in the fenestration field to use tension springs as one of the means for counterbalancing the weight of single or double hung, vertically slidable window sash. Numerous techniques have been utilized in conjunction with such springs to provide a sash support which will hold the sash stationary in any given vertical position when the operator releases it, yet permit the operator to raise or lower it with minimal effort. Such balance systems employ a variety of techniques to assure that the sash will remain stationary when released by the operator and yet can be moved either upward or downward with reasonable ease by the operator. This has been accomplished in various ways, for example those disclosed in prior U.S. Pat. Nos. 3,788,006, 4,015,367, 4,570,382, 4,571,887, 4,763,447 and 4,779,380.
One problem with these prior developments is that they are more complex and more costly than is considered desirable in the construction of certain types of housing. When it has been attempted to reduce the cost, the balance devices or systems have become unreliable or unsatisfactory because they do not consistently or continuously balance the weight of the sash at all positions, and may either creep upward or downward from a selected position o else require substantial physical effort to move the sash into certain positions of adjustment. In either case, operation of the windows is frequently frustrating and difficult. Attempted solutions to overcome these difficulties have been restricted because of the stringent limitations relating to cost while maintaining simplicity of construction and the requisite reliability of operation.
A further undesirable aspect of prior tension spring and other such sash balance systems is the unesthetic and somewhat hazardous presence of the spring itself, together with related components, which is usually disposed in open visibility along each side of the jamb. While some effort has been made previously to conceal or protectively cover such spring (for example, prior U.S. Pat. Nos. 4,570,382 and 4,779,380), the resulting concealment was not complete or not effected in a way which was esthetically desirable.